1. Field of the Invention
The present invention relates to a ranging method for measuring distance between a central node and an equipment node in a beacon wireless personal area network.
2. Description of the Prior Art
Recently, wireless personal area network has become one of the popular research fields in the communication industry, and is attracting more and more attention in academic institutes. Its development is closely connected with the contribution and push of the Institute of Electrical and Electronics Engineers (IEEE). The IEEE defines multiple beacon wireless personal network standards including IEEE802.15.1 (Bluetooth), IEEE802.15.2 (supporting both wireless personal network and wireless local area network), IEEE802.15.3 (high speed wireless personal network), and IEEE802.15.4 (low speed wireless personal network supporting Zigbee). Among these, Bluetooth technology has developed to a relatively mature status, and is widely used in mobile communication equipments. High speed wireless personal network has not made a breakthrough due to certain issues in the technology and market but the IEEE802.15.4 low speed wireless personal network supporting Zigbee has become an optimal solution in the fields of industry, science and home because of its low power, long life, wide distribution, low cost, high reliability, safety and simple development process. Short-distance positioning in beacon wireless personal area network is one of the applications which can make full use of the advantages of super bandwidth technology among various short-distance ranging methods.
There are two kinds of wireless personal area networks: beacon personal area network and non-beacon wireless personal area network, depending on whether the central node thereof is sending a beacon frame or not. The ranging technology in the current beacon wireless personal area network estimates the distance between a cell transmitting end and a receiving end based on a variable LQI (link quality indicator). Chinese patent Application No. 200510114212.3 and 200610097637.2 use this method. LQI is calculated by a reference variable RSSI (Received Cell Strength Indicator), but RSSI is easily affected by the environment, and thus produces unreliable final results. Moreover, since the error of this method exceeds 1 meter, this method is not precise enough for a beacon wireless personal area networks with a radius about 100 meters. At the same time, this ranging method does not consider the network resource management when ranging multiple points. Thus the ranging method based on LQI is suitable for an area location with fewer points, which means the ranging method can only determine whether the object node is in the range defined by the transmitting end as center and the working distance as radius. However, for the accurate position of the equipment node, the method based on LQI is not precise and the result is also not reliable.
The radius of the beacon wireless personal area network is about 100 meters. High ranging precision is needed for use in beacon wireless personal area networks especially in military and science research applications where the precision is required to reach millimeter order. In addition, the nodes in beacon wireless personal area networks specializing in low power usually do not have constant external power supply. Thus, to prolong the life of the whole network, the ranging method and process thereof must consider the proper use of the network resource.